Full-Thickness Cartilage Defects Are Important Independent Predictive Factors for Progression to Total Knee Arthroplasty in Older Adults with Minimal to Moderate Osteoarthritis: Data from the Osteoarthritis Initiative.

backgroundKnee osteoarthritis (OA) severity on radiographs is not a reliable predictor of symptom severity. The purpose of this study was to determine whether full-thickness defects or OA grade are predictive of the progression to total knee arthroplasty in older patients without end-stage arthritis.

methodsThis study included 1,319 adults aged 45 to 79 years (mean age [and standard deviation], 61.0 ± 9.2 years) who were enrolled in the Osteoarthritis Initiative, a prospective multicenter study with median 9-year follow-up data. All participants had Kellgren-Lawrence grade-0 to 3 (no to moderate) OA on bilateral radiographs; patients with grade-4 (severe) OA were excluded. The presence and total surface area of full-thickness cartilage defects on the tibia or the weight-bearing portion of the femoral condyle were determined. The risk of total knee arthroplasty due to defect presence and size as well as OA grade was determined with Cox proportional-hazards modeling after controlling for baseline variables including, but not limited to, age, sex, race, weight, knee alignment, symptom severity, quality-of-life scores, and activity level.

resultsFour hundred and ninety-six patients (37.6%) had full-thickness defects. The incidence of knee arthroplasty was 0.57% per person-year for adults without a full-thickness defect and 2.15% for those with a defect. After adjusting for confounders, the presence of a full-thickness defect increased the risk of total knee arthroplasty regardless of OA grade, with higher risk demonstrated for larger (≥2 cm) defects (hazard ratio [HR] = 5.27 [95% confidence interval (CI) = 2.70 to 10.3]; p < 0.001) compared with smaller (<2 cm) defects (HR = 2.65 [95% CI = 1.60 to 4.37]; p < 0.001). Compared with nonarthritic knees (grade 0 to 1), mild arthritis (grade 2) did not increase total knee arthroplasty risk (HR = 0.71 [95% CI = 0.31 to 1.60]); moderate arthritis (grade 3) increased total knee arthroplasty risk in adults without a full-thickness defect (HR = 3.15 [95% CI = 1.34 to 7.40]; p = 0.009) but not in adults with a defect (HR = 0.64 [95% CI = 0.28 to 1.49]; p = 0.30).

conclusionsFull-thickness cartilage defects were a major determinant of future knee arthroplasty in older adults with minimal to moderate OA, even after adjusting for baseline knee symptom severity. Baseline radiographic severity grade was only associated with future total knee arthroplasty risk in the absence of a full-thickness defect. LEVEL OF EVIDENCE: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.